Organophosphorus compounds are highly toxic to many organisms including humans. Such compounds including, for example, sarin, cyclosarin, soman, and tabun are also used as nerve agents for chemical warfare applications. These agents are some of the most potent toxic agents and are specific inhibitors of acetylcholinesterase (AChE). These inhibitors induce ACHE poisoning in humans corresponding to the accumulation of acetylcholine at all cholinergic receptor terminals, which results in blockage of neural signal transmissions. These nerve agents are generally classified into G agents (e.g., GD, soman; GB, sarin; and GA, tabun) and V agents (e.g., VX).
The various nerve agents differ in physical properties, for example, VX has a much lower vapor pressure than the G agents. However, the toxicity and main effects of the agents are very similar—inhibition of acetylcholinesterase that results in subsequent breakdown of the normal operation of the autonomic and central nervous systems. Rapid and reliable detection of organophosphorus compounds is of paramount importance to prevent casualties due to exposure to such compounds.
Organophosphorus compounds contain at least one phosphorous atom chemically bonded directly or indirectly to a carbon skeleton. The phosphorous atom may be a member of an organic chain or ring system in which phosphorous is bonded directly to carbon, or phosphorous may be the central atom in a functional group which in turn is bonded to a carbon containing chain or ring. Such functional groups commonly have one or more oxygen atoms or hydroxyl (—OH) groups surrounding the phosphorous atom. These compounds are generally represented by the Formula (I)
wherein R1 and R2 are independently selected from organic moieties including aliphatic groups, aromatic groups, and heterocyclic groups, and X is a leaving group which is energetically labile as an anion or a negatively charged group. The phosphorous atom of the compound exhibits the capacity to receive three functional or substituent groups in the form of R1, R2 and X, which enables a range of chemical variants to be produced including previously unknown ones with similar chemical effects.
Recent events involving terrorism around many parts of the world have highlighted the need for devices capable of detecting such dangerous organophosphorus compounds for use by both military and civilian personnel. The need for the reliable determination of these organophosphorus compounds particularly those with cholinesterase inhibiting effects has led to the development of a number of sophisticated methods, mostly involving the use of gas and liquid chromatography and mass spectrometry. Accurate detection and quantification of toxic substances is generally achievable, however at relatively high cost and extended response time. Additionally, the measurement of nerve agents in mixtures with these traditional methods requires cumbersome extraction and manipulation procedures.
Despite this need, the sensitive and chemically specific detection of organophosphorus compounds remains a significant challenge. This is due, in part, to the extreme toxicity of organophosphorus compounds: the median lethal dose for the nerve agent VX is 7 μg per kg of body weight for a normal adult, requiring sensitivity levels in the range of parts per billion.
Current methods for analyzing organophosphorus compounds having nerve agent activity have been limited, particularly with respect to previously unknown organophosphorus nerve agents. Such methods require multi-instrumental investigations, thus necessitating larger sample amounts and extensive time and effort for reliable implementation. Samples obtained from the environment can contain a range of complex organophosphorus compounds generated from biological and industrial sources. The labile nature of such compounds requires a rapid method of analysis.
It would be useful to have a detection mechanism with features, which are applicable to both military and commercial product markets including cost effectiveness, high reliability and capability of identifying organophosphorus compounds. Satisfying these demanding requirements necessitates a novel approach to the measurement of low concentrations of organophosphorus compounds including those previously unknown. There is a further need to provide a rapid, efficient and highly reliable method of detecting, identifying and quantifying known and prospective chemical agent threats specifically organophosphorus based nerve agents and their corresponding degradation products.